With increasing concern about global environmental problems, interest in solar cells has been increasing in recent years. Solar cells are mostly installed outdoors in the form of a solar-cell module, which generally has a structure comprising a solar-cell panel and a frame into which the panel is fitted. FIGS. 4(A) and 4(B) shows the structure of such a conventional solar-cell module.
FIG. 4(A) is a plan view of a representative example of conventional solar-cell module structures and FIG. 4(B) is a sectional view taken on line B--B in FIG. 4(A). As shown in these figures, a conventional solar-cell panel 56 has generally employed a structure wherein solar-cell elements 53 disposed on a light-transmitting plate 50 on the side opposite to the sunlight-receiving surface are coated with a filler material 52, e.g., an ethylene/vinyl acetate copolymer (hereinafter referred to as "EVA"), and then covered with a back sheet 54 made of poly(vinyl fluoride) (hereinafter referred to as PVF). The solar-cell module 60 comprises a frame 59 composed of four aluminum frame members 58 which is fitted to the peripheries of the solar-cell panel 56. For fixing the solar-cell panel 56 to the frame 59, a sealant 62 such as butyl rubber, which is a tacky consistency material at ordinary temperature, is used to fit and fix the peripheries of the solar-cell panel 56. The solar-cell modules thus produced are fixed to an outdoor supporting structure with screws through installation holes 64 formed in the frame 59. Thus, a solar-cell array is constructed.
Use of a combination of a silicone sealant and a butyl rubber sealant in place of the butyl rubber used as the sealant has been proposed as described in unexamined published Japanese Utility Model Application No. Hei-4-130457.
However, the conventional solar-cell module 60 having the foregoing structure has the three major problems described below.
First, because of the manner in which the frame 59 is fitted to the solar-cell panel 56, the process for producing the solar-cell module 60 is complicated and this results in increased fluctuations in the external dimensions of the solar-cell module 60. As shown in the figure, in producing the conventional solar-cell module 60, the peripheries of the solar-cell panel 56 are fitted into U-shaped recesses of the four frame members 58 constituting the frame 59. Therefore, in the case where the solar-cell module 60 is rectangular, the four frame members 58 should be respectively fitted to the four peripheries of the solar-cell panel, as shown in FIG. 4(A), and be then fixed to one another with screws or by another means to construct the frame 59. That is, the first problem is that the fabrication procedure requires much time and labor. Moreover, the presence of the butyl rubber sealant 62 between the solar-cell panel 56 and the frame 59 has resulted in a drawback that the external dimensions of the solar-cell module 60 fluctuate as the thickness of this sealant layer 62 varies. Such fluctuations in the external dimensions of the solar-cell module 60 cause troubles in the fabrication of a solar-cell module array because of the shifting of the relative positions of the installation holes 64 and the outdoor supporting structure.
The second problem concerns the tacky consistency of the butyl rubber sealant at room temperature. If the solar-cell module 60 is exported to tropical areas, the packaged solar-cell module 60 heats up during use and, as a result, the butyl rubber sealant deforms or softens.
The use of butyl rubber in combination with, e.g., a moisture-curing silicone sealant at ordinary temperature is effective in eliminating the second problem described above. However, there is the third problem in that since the sealant is pasty at ordinary temperature and cures upon reaction with moisture, it remains in an uncured pasty state immediately after the fabrication of the solar-cell module 60, whereby the relative positions of the solar-Cell panel 56 and the frame 59 may shift due to slight vibrations caused by transport, stacking, and so on. Because of this, the solar-cell module 60 should be aged for from several hours to several days until the sealant cures, resulting in a low production efficiency.
As described above, the structure of the frame 59, the use of a butyl rubber sealant, and the use of a butyl rubber sealant and a silicone sealant in combination have caused serious problems concerning not only the quality of the conventional solar-cell module 60 but also the process for producing the module.